Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications. In order to reduce complications, one of the goals of treatment is to maintain maternal blood glucose levels within as close to normal range as possible. For some women with GDM, insulin is required to achieve optimal blood glucose levels; however, most women with GDM do not receive medication and are "diet-controlled". Despite this, there is little evidence about the optimal composition of macronutrients in the diet for women with GDM. The proposed randomized controlled trial is designed to test the hypothesis that a lower carbohydrate diet will help pregnant women with GDM to achieve better blood glucose control and reduce the rate of serious complications for themselves and their infants. Potential subjects will be screened for GDM with a 50 gm, 1-hour glucose challenge test. Women whose 1-hour screening test result e 135 mg/dl will undergo a 100 gm, 3-hour glucose tolerance test as per American Diabetes Association (ADA) guidelines. Diagnosis of GDM will be conferred if 2 or more abnormal values are found with the 100 gm test. Women diagnosed with GDM will be eligible to enter the study and randomized into one of two groups: those who are placed on a lower carbohydrate diet (between 35-40 percent of total calories) versus a usual care (control) group. Subjects in both groups will be instructed in blood glucose self-monitoring with portable reflectance memory meters. Women will be asked to monitor their blood glucose levels 4 times daily (fasting and 1- hour after meals). Statistical analyses will be based on intention to treat. The Student's t- test for independent samples will be used to determine if there are differences in the means of continuous variables between the 2 groups, including the primary outcome variable of mean postprandial blood glucose values. The Fisher's exact test will be used to compare categorical variables, such as rates of maternal complications for women with GDM. Infant outcome measures will include birth weight and rates of complications commonly found in infants of mothers with GDM. The clinical site for the proposed study serves a population at higher risk for health disparities and for developing GDM, with patients who are primarily African-American and Hispanic. Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications. Most often controlled by diet, there is little evidence as to what constitutes the best diet for a mother with GDM. This study will evaluate the impact of a lower carbohydrate diet on the health of mothers with GDM and their infants when they are compared with a "usual care diet" control group. [unreadable] [unreadable] [unreadable] [unreadable]